1. Field of the Invention
The invention relates to an iron based sintered body, particularly to an iron based sintered body excellent in enveloped casting property in a light metal alloy. The iron based sintered body is used as being enveloped in a light metal alloy member such as an aluminum alloy by casting.
2. Description of the Related Art
Automobile parts made of an aluminum alloy as a kind of light metal alloys are widely used for making the automobile parts lightweight and for enhancing heat-release ability thereof. However, the aluminum alloys are insufficient in material characteristics as automobile structural members including poor mechanical properties such as strength, wear resistance and rigidity as well as high thermal expansion coefficient as compared with usually used cast iron.
For improving the material characteristics of the aluminum alloy members, different kind of materials are enveloped in the aluminum alloy member by casting such as, for example, gravity casting and die casting, or the aluminum alloy member is compounded with different kind of materials.
For example, Japanese Patent Application Laid-Open (JP-A) No. 60-219436 proposes an engine block having a bearing member of an aluminum alloy housing cap which is formed by enveloping an iron based material by casting. The aluminum alloy housing cap is attached under a main body of an aluminum alloy cylinder block. According to the art described in JP-A No. 60-219436, the mechanical strength is enhanced to an extent not attainable by using only the aluminum alloy with a large improvement of rigidity, and a proper amount of the clearance change by a difference of the thermal expansion coefficient between the bearing and the crank shaft is maintained.
Japanese Utility Model Application Laid-Open (JP-U) No. 63-150115 proposes a crank shaft supporting member of an internal combustion engine made of a light metal alloy. The inside of a portion of the supporting member partitioned with a center lines of bolt holes for mounting on a cylinder block and a curved crank journal supporting surface is reinforced with reinforcing fibers.
JP-A 2001-276961 describes an art for producing a composite member impregnated with an aluminum alloy by a casting method, wherein molten aluminum alloy is allowed to permeate into a porous metal premolded body containing 10 to 40% by weight of chromium in iron or iron based alloy with a given time lag after completing injection of molten aluminum.
Japanese Patent Application Publication (JP-B) No. 2-30790 proposes a method for producing an aluminum alloy casting by applying an intermetallic compound forming treatment, wherein a porous metal body is placed in a mold, the porous metal body is enveloped in an aluminum alloy by casting by a high pressure solidification casting method, and a layer of a compound between aluminum and metal element of the porous metal body is formed by heating at 450 to 550° C. According to the art described in JP-B No. 2-30790, a high bonding strength between the porous metal body and aluminum alloy is obtained with improved durability.